The developers/posters on this forum/basically everyone lacks procedure for determining what's "plausible" in game-context, because the game's context allows outcomes quite wildly different from the historical scenario at a given year. The devs do it based on whim/believing it might be fun/whatever and people mostly argue from hindsight bias rather than any coherent reasoning.
When you get right down to it though, the European cardinal restriction doesn't make sense in historical or game terms. It's the kind of thing that prevents "kingdom of Jerusalem" from having cardinals in the vast majority of its empire while a Japan that conquers through Persia and owns some of the Caucuses + Russia can have the maximum 7 cardinals available to a country, even though the country wasn't even Catholic 25 years prior.
One could just restrict it from colonial governments and call it a day, or do something else entirely. Its current implementation is awkward though. I don't miss the micromanagement of the old setup at all, but it did make more sense wrt gameplay because the giant Catholic nations put investment into their curia and who had the influence was based on consistent criteria + strength of a Catholic nation. Right now, a nation could be triple the size of any other Catholic power in the world and be locked into having 0 cardinals, even if the Papal State is allied to them. That's not intuitive at all

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